基于SSH的安全远程登录_openssh远程登录

一、SSH：Secure Shell

实现的软件工具
1.Openssh：centos默认安装

相关包：

• openssh
• openssh-clients
• openssh-server

配置文件：
客户端：/etc/ssh/ssh_config
服务器端：/etc/ssh/sshd_config

2.Dropbear：开源工具

基于C/S结构
Linux Client: ssh, scp, sftp，slogin
Windows Client：xshell, putty, securecrt, sshsecureshellclient
Server: sshd

二、Openssh

配置文件路径下的文件：私钥、公钥存放位置

[root@CentOS7 ~]#ll /etc/ssh/
total 604
-rw-r--r--. 1 root root     581843 Apr 11  2018 moduli
-rw-r--r--  1 root root       2305 Jul 16 20:09 ssh_config
-rw-------. 1 root root       3907 Apr 11  2018 sshd_config
-rw-r-----. 1 root ssh_keys    227 May 11 14:22 ssh_host_ecdsa_key
-rw-r--r--. 1 root root        162 May 11 14:22 ssh_host_ecdsa_key.pub
-rw-r-----. 1 root ssh_keys    387 May 11 14:22 ssh_host_ed25519_key
-rw-r--r--. 1 root root         82 May 11 14:22 ssh_host_ed25519_key.pub
-rw-r-----. 1 root ssh_keys   1675 May 11 14:22 ssh_host_rsa_key #私钥文件，服务器级私钥
-rw-r--r--. 1 root root        382 May 11 14:22 ssh_host_rsa_key.pub #公钥文件，服务器级公钥
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第一次连接确认身份需要人工确认，连接公网主机时，需要自己计算哈希值，是否与公开的哈希值相同

两种登录认证方式：
1.基于密码:每次连接需要手工输入密码
2.基于key:不需要输入密码

（一）基于密码登录：

1.客户端配置

（1）客户端第一次连接服务，会弹出是否连接的提示，可在客户端配置中选择是否弹出提示

[root@CentOS7 ~]#vim /etc/ssh/ssh_config 
StrictHostKeyChecking no
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家目录生成文件：连接时在提示后面敲完yes，或者客户端设置不提示，会在客户端家目录~/.ssh下生成一个known_hosts 文件；用于Client和Server的双向认证，避免中间人（man-in-the-middle attack）攻击；每次Client向Server发起连接的时候，SSH client通过known_hosts中的host key来验证Server的身份的

[root@CentOS7 ~]#cat .ssh/known_hosts 
#格式:DomainName/IpAddress EncryptionAlgorithm HostKey
192.168.37.100 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBPmD8LimHeC8phXcEzH6qOqcdzB0b2xYNN08trPfwBH1HhZf7uG87lhr2b8Ca7ocZ4J+Q9nyMxvufvD3Pm4CPF0=
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（2）SSH 客户端使用
常用连接登录语法：

ssh [user@] host [COMMAND]
ssh [-l user] host [COMMAND]
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常用选项：
-p port：远程服务器监听的端口
-b：指定连接的源IP，如果客户端有多个IP，可指定某个IP连接服务器
-v：调试模式
-C：压缩方式，节约带宽
-X：支持x11转发，X协议，依赖xserver服务
-t：强制伪tty分配

ssh 默认以当前用户名连接远程主机

[root@CentOS7 ~]#ssh root@192.168.37.100 cat /etc/passwd
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-b: 客户端指定IP连接服务器端

服务器端查看连接的主机IP：

-v： 调试模式，查看登录过程

[root@CentOS7 ~]#ssh root@192.168.37.100 -p 2222 -b 192.168.37.7 -v
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips  26 Jan 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 59: Applying options for *
debug1: Connecting to 192.168.37.100 [192.168.37.100] port 2222.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 192.168.37.100:2222 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:j+FKSoZLTx3S9cFLtPfZWnJUCrx9cAONPuCAsS7hfgo
debug1: checking without port identifier
debug1: Host '192.168.37.100' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:1
debug1: found matching key w/out port
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:0)

debug1: Unspecified GSS failure.  Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:0)

debug1: Next authentication method: publickey
debug1: Trying private key: /root/.ssh/id_rsa
debug1: Trying private key: /root/.ssh/id_dsa
debug1: Trying private key: /root/.ssh/id_ecdsa
debug1: Trying private key: /root/.ssh/id_ed25519
debug1: Next authentication method: password
root@192.168.37.100's password:
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-X： xclock 是X协议的客户端，xserver服务按照客户端指令，通过显卡GPU绘图；
xclock客户端和xserver可能不在同一台主机
xmanager（包含xshell）安装时给window安装xserver，windows本身不带xserver

-t:类似跳板机，直接跳到某个主机

#最后一个主机不加-t
[root@master ~]#ssh -t 192.168.37.102 ssh -t 192.168.37.103 ssh 192.168.37.101
root@192.168.37.102's password: 
root@192.168.37.103's password: 
root@192.168.37.101's password: 
Last login: Tue Jul 16 21:15:09 2019 from 192.168.37.103

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2.服务器端：
修改ssh端口号：生产环境如果是基于口令登录的，建议修改端口

[root@master ~]#vim /etc/ssh/sshd_config
 Port 2222 
[root@master ~]#systemctl restart sshd

#客户端连接指定服务器端口
#[root@CentOS7 ~]#ssh root@192.168.37.100 -p 2222
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（二）基于Key的登录验证

测试环境：
两台centos7 主机：IP分别为192.168.37.102、192.168.37.103
192.168.37.102 为客户端
192.168.37.103 为服务端主机

配置如下：
1.手动生成公钥、私钥：基于用户级的秘钥对，每个用户有不同的自己的秘钥对；
配置过程中传输公钥时，仍然需要基于密码验证

#192.168.37.102主机操作生成秘钥对
[root@CentOS7 ~]#ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):   #设置保存秘钥路径
Enter passphrase (empty for no passphrase):  #设置私钥密码
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:FJaHeE4S+F++zu1RcgUhu6aE81atdUsRFsBlB5heWcw root@CentOS7.6.localdomain
The key's randomart image is:
+---[RSA 2048]----+
|     ..ooo  o+*&+|
|    . o.=.. o+=.E|
|     . =.. ... ..|
|      ..... .o ..|
|       .So. = =..|
|        .+.+ *...|
|          +.o  . |
|         o.. .   |
|         .o.o    |
+----[SHA256]-----+

[root@CentOS7 ~]#ll .ssh/
total 16
-rw------- 1 root root 1675 Jul 16 22:25 id_rsa     #ssh-keygen生成的私钥
-rw-r--r-- 1 root root  408 Jul 16 22:25 id_rsa.pub  #ssh-keygen生成的公钥
-rw-r--r-- 1 root root  748 Jul 16 21:11 known_hosts

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2.拷贝主机公钥

#102主机第一次拷贝时需要输入口令
[root@CentOS7 ~]#ssh-copy-id -i /root/.ssh/id_rsa.pub root@192.168.37.103

#37.103主机查看家目录文件，拷贝过来的公钥系统改名为authorized_keys
[root@CentOS7 ~]#ll ~/.ssh/
total 8
-rw------- 1 root root 408 Jul 16 22:30 authorized_keys  #37.102主机的公钥，大小相同
-rw-r--r-- 1 root root 396 Jul 16 21:12 known_hosts

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102主机 /root/.ssh/id_rsa.pub 和103主机 /root/.ssh/authorized_keys 公钥文件内容相同
3.测试登录

#102主机测试登录103主机
[root@CentOS7 ~]#ssh 192.168.37.103
Last login: Tue Jul 16 21:24:08 2019 from 192.168.37.102
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